Facebook has begun the arduous work of shutting down Arabic-language pages created for selling ancient Syrian artifacts ransacked from areas controlled by the Islamic State (ISIS/ISIL/IS). The sale of priceless antiques has become a cornerstone of the ISIS economy, as demand skyrockets for the contents of looted museums, temples, and ruins.

D.C.-based journalist Zaid Benjamin has posted screenshots of a number of screenshots allegedly showing Facebook pages, most already taken down, promising the sale of a variety of ancient items–from statuettes to coins and manuscripts. Some of the images only show the artifacts themselves and do not indicate the pages from which they were taken:

Argentine website Infobae, which republished the photos, notes that some of the images depicted are up to 10,000 years old and can sell for as much as $1 million each on the black market. They note that reports have indicated these are sold with permission from Islamic State jihadists, who have stolen them from museums and archaeological sites that they have now conquered. Merchants who sell these on the black market in Turkey and elsewhere are required to pay ISIS an extra tax for doing so, they report, estimated at between 20% and 50%.

This is not the first such report of antiques appearing online, having surfaced from ISIS-controlled areas. In March, the International Business Times reported that similar items, including jewelry, had begun surfacing on the auction site eBay. They noted one listing in particular, that offered two ancient Syrian coins for $84 and $133 each.

Coins and small statues are the most valuable, experts told the IB Times, because they are easily smuggled in and out of countries, and are found in larger amounts.

The more lucrative, larger, or more dangerous-to-smuggle items are sometimes sold by word of mouth, interest reaching the ears of collectors at legal auctions. TheWashington Postreported in February that British buyers had begun to be courted by sellers proposing “interesting” goods that had just arrived from Syria and Iraq. “I get approached all the time about looted artifacts, whether it’s directly from someone who’s trying to sell it or images that were sent to somebody who has offered to buy it,” said Christopher Marinello, director of Art Recovery International. The Post described the items offered as “old and silver Byzantine coins as well as Roman pottery and glass worth hundreds of thousands of dollars.” It estimates about 100 items have made their way to the UK.

The Islamic State has destroyed millions of dollars in priceless archaeological and heritage sites in the name of opposing idolatry and destroying any religious site dedicated to anyone but Allah. In the most harrowing display of this practice, the group released a video in January of jihadists using hammers to destroy artifacts in the Museum of Mosul, Iraq’s second-largest city. Not all the ancient Assyrian art destroyed, however, was original; many were replicas, with the originals safely preserved elsewhere.

Standing between the Islamic State and the destruction or disappearance of Assyrian cultural heritage is a small group of “graying academics,” nicknamed Syria’s “monuments men,” who have taken on the mission of finding as many artifacts as possible before the Islamic State does and moving them to safe areas. “It’s dangerous work. We have to get in and out of a site very quickly,” he claims. “The looting has become systematic, and we can’t keep up.”

In addition to the sale of artifacts, Facebook has had to shut down numerous pages set up dedicated to selling young Syrian women, whose families have fled the civil war and have found no other way to make money. One page, titled “Syrian Refugees for Marriage,” was shut down after 18,000 users “liked” it; it is not known whether the page managed to sell any brides before it was shut down.